Re: PHOTOS: CALTRAN CALTRAIN IV

Ok, RIVERline is obviously light rail, but why is that? What if instead of light rail vehicles they had chosen to go with a locomotive/un-powered coach arrangement? Is that the only thing differentiating light rail from commuter rail in that instance?

Although there may be a fuzzy line between modes,generally outside of the boundary area there is no doubt as to the definition. The NYC Subway is definitely NOT commuter rail,for example.

NYC is the perfect example actually. While we all know what's subway, and what's commuter rail, the main differences are fleet type, Fare collection method and signal system (what is SIRT anyway?) However, the cost savings advantages of 'minimums of modality' are practically non-existant. LIRR needs high platforms, within the city limits is generally grade separated, and requires a signal system that can handle the kind of headways generally associated with Rapid Transit systems. This all speaks to the point that you can't compare capital costs purely based upon mode; a case by case analysis must be made.

Using the criteria you stipulated previously for commuter rail (low platforms, lack of grade separation, 'advanced' signalling not necessary), one could argue that the most overlap is actually between light rail and commuter rail.